通过晶体结构预测和NMR晶体学的联合努力揭示两种呋咱多晶型物的晶体结构
Crystal structures of two furazidin polymorphs revealed by a joint effort of crystal structure prediction and NMR crystallography
摘要：
在这项工作中，我们提出了晶体结构测定的两个难以捉摸的多晶型呋咱，抗菌剂，采用晶体结构预测（CSP）计算和NMR晶体学方法相结合。两个先前未表征的纯晶体形式，其中一个具有两个对称性独立的分子（形式I），而另一个只有一个分子（形式II），分别在P21/c和P-1空间群结晶，并且都由不同的构象异构体构建，显示不同的分子间相互作用。我们证明，无论是晶体结构预测或NMR晶体学单独使用是不够的，以成功地阐明上述晶体结构，特别是在两个独立的分子的多晶型结构的情况下。此外，分析和描述了在晶体结构预测中获得的1H或13 C NMR数据与实验室中观察到的晶体结构不同（假阳性匹配）的偶然协议的情况。尽管对于大多数分析的晶体结构，与NMR实验的一致性表明了与实验结构相同的一些结构特征，但在例外情况下观察到的上述意外发现表明，在晶体结构测定中使用NMR晶体学方法时必须谨慎。
英文摘要：
In this work we present crystal structure determination of two elusive polymorphs of furazidin, an antibacterial agent, employing a combination of crystal structure prediction (CSP) calculations and NMR crystallography approach. Two previously uncharacterized neat crystal forms, one of which has two symmetry independent molecules (form I), whereas the other one has only one molecule (form II), crystallize in P21/c and P-1 space groups, respectively, and are both built by different conformers, displaying different intermolecular interactions. We demonstrate that the usage of either crystal structure prediction or NMR crystallography alone is insufficient to successfully elucidate the mentioned crystal structures, especially in the case with two independent molecules in the polymorph structure. In addition, cases of serendipitous agreement in terms of 1H or 13C NMR data obtained for the crystal structure prediction generated crystal structures different from the ones observed in laboratory (false-positive matches) are analyzed and described. Although for majority of analyzed crystal structures the obtained agreement with the NMR experiment is indicative of some structural features in common with the experimental structure, the mentioned serendipity observed in exceptional cases points to the necessity of caution when using NMR crystallography approach in crystal structure determination.
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